An amorphous oxide semiconductor used in a TFT has a higher carrier mobility as compared with a general-purpose amorphous silicon (a-Si), has a large optical band gap and can be formed into a film at lower temperatures, and hence, is expected to be applied to a next-generation display that requires an increase in size, an increase in resolution and high-speed driving or to a resin substrate having low heat resistance, etc. When forming the above-mentioned oxide semiconductor (film), a sputtering method in which a sputtering target formed of the same material as that of said film is sputtered is preferably used. The reason therefor is that, as compared with a thin film formed by ion plating method, vacuum vapor deposition method or electron beam evaporation method, a thin film formed by a sputtering method has excellent in-plane uniformity of a component composition in the film surface direction, a film thickness, etc., whereby a thin film having the same component composition as that of the sputtering target can be formed. The sputtering target is normally formed by mixing oxide powder, sintering the mixture, followed by mechanical processing.
An In—Ga—Zn—O amorphous oxide semiconductor containing In is an oxide semiconductor that has most developed as an oxide semiconductor used in a display (see Patent Documents 1 to 4, for example). Further, in recent years, in order to attain high mobility or improve reliability of a TFT, an attempt is made to use In as a main component and to change the type or concentration of added elements (see Patent Document 5, for example).
In Patent Documents 6 and 7, an In—Al-based sputtering target is reported.
In Comparative Example 6 of Patent Document 8, an oxide thin film having a composition of Al/(In+Al)=0.125 is described.